1. Field of the Invention
The present invention relates to shoe sole and heel constructions and, in particular, to such constructions with fluid-filled cavities for providing cushioning and forward thrust.
2. Description of the Prior Art
Various types of shoe sole and heel constructions having fluid-containing cavities have heretofore been provided, such constructions being disclosed, for example, in U.S. Pat. Nos. 4,237,625, 4,358,902 and 4,577,417. The present invention is, in particular, an improvement of the construction disclosed in U.S. Pat. No. 4,577,417, which discloses a molded outer sole and heel member which has heel and metatarsal bulges molded therein to define cavities and a passageway extending between the cavities. Air, at atmospheric pressure, moves back and forth between the cavities through the passageway during movement of a person wearing the shoe.
These prior sole and heel structures have provided cushioning for the user's foot and have also provided forward thrust which facilitates walking or running movements. One difficulty which has arisen with respect to such prior shoe sole and heel constructions is that the bulges may tend to produce a lateral instability in the shoe, causing the shoe to tilt laterally inwardly or outwardly in use, resulting in pronation of the wearer's feet. For example, in walking and jogging gaits, wherein the initial shoe strike is at the heel, the initial point of impact is typically at the laterally outer side of the heel, i.e., at the right side of the right heel and the left side of the left heel. Thus, there is a tendency for the fluid in the heel cavity to move from side to side, as well as toward the metatarsal cavity.
Furthermore, it has been found that better control is needed of the time, location and direction of the air flows within the shoe sole and heel construction to improve the cushioning effect.